Blowing agent mixture

ABSTRACT

The invention refers to a blowing agent composition consisting of 1,4 butan-diol-bis-(carbonic acid ester-benzoic acid anhydride) and silicon dioxide. Silicon dioxide reduces the decomposition temperature of the anhydride while at the same time increasing the yield of gas substantially.

This invention relates to a blowing agent mixture based on1,4-butane-diol-bis-(carbonic acid ester-benzoic acid anhydride) and toa process for the production of thermoplastic resin foams.

The expansion of thermmoplastic melts by decomposition of a blowingagent has become widely used for the production of moulded foam resins.1,4-butanediol-bis-(carbonic acid ester-benzoic acid anhydride) hasalready been used as blowing agent for this purpose. The use of thisproduct for the production of foams from thermoplasts has been describedin German Pat. No. 1,252,891.

The low melting point of 1,4-butanediol-bis-(carbonic acid ester-benzoicacid anhydride), which is only 77° C, however, stands in the way of itswider use. When the dried thermoplast granulates are ready forprocessing and are mixed with the blowing agent while they are stillhot, the blowing agent melts and causes the formation of lumps in thegranulate which give rise to difficulties in mixing and dosing.Furthermore, the decomposition products of the blowing agent affect theaverage molecular weight of certain thermoplasts. The demand forcompatibility of the molten thermoplast with the blowing agent and itsdecomposition products may be met more easily in polymers, such aspolyolefines or polyvinyl chloride, which are resistant to saponifyingagents than in polycondensates, such as polycarbonate based on bisphenolA. The decomposition products of 1,4-butanediol-bis-(carbonic acidester-benzoic acid anhydride) have an adverse effect on the averagemolecular weight of polycarbonates based on bisphenol A. The reductionin average molecular weight increases with increasing decompositiontemperature and with increasing concentration of the blowing agent.

It was an object of this invention to develop a blowing agent based on1,4-butanediol-bis-(carbonic acid ester-benzoic acid anhydride) whichwould not have the disadvantages described above. It has now been foundthat the addition of finely divided silicon dioxide activates thedecomposition of 1,4-butane-diol-bis-(carbonic acid ester-benzoic acidanhydride). The decomposition temperature is reduced by up to 30° C andthe yield of blowing gas is increased by up to 20%. It could also befound that the reduction in average molecular weight of thepolycarbonate based on bisphenol A is very limited. Thus, mouldedpolycarbonate foam products produced from polycarbonate with the aid ofthe blowing agent mixture according to the invention have a higher levelof mechanical properties, such as impact strength, for example, thanmoulded polycarbonate foam products of the same density which have beenfoamed with 100% 1,4-butanediol-bis-(carbonic acid ester-benzoic acidanhydride). Moreover, the moulded products produced with the aid of theblowing agents according to the invention have an extremely fine porestructure.

This invention therefore relates to a blowing agent mixture consistingof 1,4-butanediol-bis-(carbonic acid ester-benzoic acid anhydride) andsilicon dioxide. Another object of this invention is the application ofthis blowing agent mixture to the production of foamed moulded productsof thermoplastic resin.

1,4-butanediol-bis-(carbonic acid ester-benzoic acid anhydride) mayeasily be obtained by the process according to German Pat. No.1,133,727. The silicon dioxide used preferably has a surface areaaccording to B.E.T. of from 50 to 400 m² /g, more preferably from 300 to350 m² /g. The surface is measured by the known process of BRUNAUER,EMMET and TELLER. This process has been described in "The Journal of theAmerican Chemical Society" 1938,Volume 60, page 309.

The silicon dioxide preferably has a water content of less then 1.5%, byweight. The water content may be determined by the weight loss after 2hours' drying at 150° C. The proportion of pure silicon dioxide shouldpreferably be greater than 99.8%. The weight loss after 2 hours'annealing at 1000° C should preferably be less than 2.5%.

The preparation of blowing agents may be obtained by mixing thecomponents in the conventional manner, for example, by milling. It maycontain any proportion of silicon dioxide, but preferably from 0.5 to70%, by weight, and, in particular, from 15 to 40%, by weight. Theproportion of 1,4-butanediol-bis-(carbonic acid-benzoic acid anhydride)in preferred examples of the product is therefore from 99.5 to 30%, byweight, and especially from 85 to 60%, by weight.

The blowing agent mixture according to the invention is suitable forblowing thermoplastic resin melts, but particularly for foaming polymerswhich require to be blown at temperatures above 180° C. Thermoplasts ofthis type include, e.g. polycarbonates, polyesters, polyamides andmixtures of polyphenylene ethers and polystyrene.

Granulates of the thermoplast are mixed with the blowing agent mixtureand heated to a temperature above the decomposition temperature of theblowing agent preparation and above the softening temperature of thethermoplast. The thermoplast melt is thereby foamed by the decompositionof the blowing agent preparation. The foaming temperature employed maybe, for example, from 160° to 300° C.

The proportion of blowing agent mixture in the thermoplastic materialwhich is required to be foamed may vary over a wide range and issuitably from 0.1 to 15%, more preferably from 0.5 to 5%, by weight,based on the finished mixture of thermoplastic granulate and blowingagent preparation.

The blowing agent preparation is preferably mixed into the dried resingranulate which is ready for use. The finished mixture may containcolourless or coloured unreinforced and/or reinforced thermoplastgranulates as well as additives, such as colouring agents, stabilizers,fillers, glass fibres, flame retarding additives, as well as otherblowing agents which split off carbon dioxide and/or nitrogen, e.g.azodicarbonamie, isophthalic acid-bis-carbonic acid ethyl esteranhydride), benzazimides and decomposition accelerators, such as zincnapthenates, zinc oxide, magnesium oxide, cobalt naphthenates andbenzene sulphinates.

These mixtures of thermoplastic resins and blowing agent mixtureaccording to the invention, which optionally contain other additives,may be shaped from the resin melt by the conventional processes ofshaping hollow or solid bodies, e.g. injection moulding, extrusioncasting or rotatonal moulding.

The temperature range within which the blowing agent preparationaccording to the invention undergoes decomposition may vary with theamount of finely divided silicon dioxide and other additives containedin the preparation and with the nature of the thermoplastic resin used.The decomposition range for the blowing agent preparation according tothe invention is generally from 160° to 240° C. The decompositionvelocity is preferably from 15 to 90 seconds for 100 ml of blowing agentgas measured at room temperature at normal pressure per gram of blowingagent preparation.

The polycarbonates which may be foamed in this way include, for example,the polycondensates which can be obtained by the reaction of aromaticdihydroxy compounds, in particular dihydoxydiarylalkanes, with phosgeneor diesters of carbonic acid, but not only unsubstituteddihydroxydiarylalkanes are suitable for the preparation of thesepolycondensates, but also dihydroxydiarylalkanes in which the arylgroups carry methyl groups or halogen atoms in the ortho- and/ormeta-position to the hydroxyl group. Branched polycarbonates are alsosuitable.

The polycarbonates which may be foamed have average molecular weightsof, e.g. from 10,000 to 100,000 and more preferably from 20,000 40,000 .

The following are examples of suitable aromatic dihydroxy compounds:hydroquinone, resorcinol, 4,4'-dihydroxydiphenyl,bis-(hydroxy-phenyl)-alkanes, such as C₁ -C₈ alkylene or C₂ -C₈alkylidene bisphenols, bis-(hydroxypenyl)-cycloalkanes, such as C₅ -C₁₅cycloalkylidene bisphenols, bis-(hydroxyphenyl) sulphides, -ethers,-ketones, -sulphoxides or -sulphones, as well asα,α'-bis-(hydroxyphenyl)-diisopropylbenzene and the correspondingcompounds which are alkylated or halogenated in the nucleus.Polycarbonates based on bis-(4-hydroxyphenyl) -propane-(2,2) (bisphenolA), bis-(4-hydroxy-3,5-dichlorophenyl-propane-(2,2)(tetrachlorobisphenol A),bis-(4-hydroxy-3,5-dibromophenyl) -propane-(2,2)(tetrabromobisphenol A),bis-(4-hydroxy-dimethyl-phenyl) -propane (2,2) (tetramethylbisphenol A),bis-(4hydroxyphenyl)-cyclohexane-(1,1) (bisphenol Z) and those based ontrinuclear bisphenols, such as α,α'-bis-(4-hydroxyphenyl)-p-diisopropylbenzene, are preferred.

Other aromatic dihydroxy compounds which are suitable for thepreparation of polycarbonates have been described in U.S. Pat. Nos.3,028,365; 2,999,835; 3,148,172; 3,271,368; 2,970,137; 2,991,273;3,271,367; 3,280.078; 3,014,891 and 2,999,846.

The polyamides which are to be foamed may be condensation productscontaining recurrent amide groups are constituents of the polymer chain.They can be prepared by polymerising a monoamino-monocarboxylic acid orinternal lactam thereof, such as caprolactam, amino-undecanoic acid oraluric lactam, or by condensing a diamine, such as hexamethylenediamine, trimethylhexamethylene diamine or octamethylene diamine, withdicarboxylic acids, such as adipic acid, decanedicarboxylic acid,isophthalic acid or terephthalic acid.

Polyesters which are to be foamed may be, e.g. saturated linearpolyesters of terephthalic acid with an intrinsic viscosity of from 0.5to 1.5 dl/g in which the dicarboxylic acid component contains ≦90 mol %of terephthalic acid and the glycol component ≦90 mol % of glycols ofthe C₂ to C₁₀ series.

Mixtures of polyphenylene ethers and polystyrene which may be foamed arethermoplastic compounds consisting of a polyphenylene ether and arubber-modified, impact resistant polystyrene which contains a finelydivided elastomeric gel phase dispersed in a polystyrene matrix. Thepolyphenylene ether consists of recurrent units of the followingstructure: ##STR1## wherein the oxygen ether atoms of one unit isattached to the benzene ring of the adjacent unit; n represents 50; andeach radical Q represents a monovalent substituent, such as hydrogenatoms, halogen atoms, hydrocarbon groups, halogenated hydrocarbongroups, alkoxy groups and halogenated alkoxy groups. The polystyrenematrix resins are derived from a monovinyl aromatic monomer, e.g. onerepresented by the following general formula: ##STR2## wherein Rrepresents hydrogen, alkyl or halogen; Z represents hydrogen, halogen oralkyl; and p = 0 or an integer of from 1 to 5. The elastomeric gel phaseconsists of polybutadiene and/or a copolymer of butadiene and styrene ora mixture of polybutadiene and this copolymer.

Other substances suitable for the preparation of such mixtures have beendescribed in U.S. Pat. No. 3,383,435 and in German OffenlegungsschriftNos. 2,342,119; 2,255,930; 2,211,006; 2,211,005; 2,136,838; 2,119,301and 2,000,118.

The nature of the invention will now be explained more fully with theaid of the following Examples.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a plot of gas evaluation measured in ml versus temperaturein degrees Celsius for 1,4-butane diol-bis-(carbonic acid ester benzoicacid anhydride) and two blowing agent mixtures of the present invention.

EXAMPLE 1

The evolution of gas from the blowing agent as a function of thetemperature was determined in a standard apparatus (flask, pneumatictank). This apparatus does not give absolute values but only relativevalues. It is therefore suitable for comparison tests.

The following blowing agents were tested:

1. 2.00 g of 1,4-butanediol-bis-(carbonic acid ester-benzoic acidanhydride), 100%;

2. 1.48 g of 1,4-butanediol-bis-(carbonic acid ester-benzoic acidanhydride), 100%, + 0.52 g of silicon dioxide which has a surface offrom 270 to 330 m² /g according to BET and a water content of 1.5%. Thissilicon dioxide is manufactured by Degussa under the trade name "Aerosil300";

3. 2.000 g of 1,4-butanediol-bis-(carbonic acid esterbenzoic acidanhydride), 100% + 0.7 g of silicon dioxide (same quality as describedunder 2).

The graphs in FIG. 1 represent the liberation of gas as a function ofthe temperature for the three blowing agents indicated above. They showthat the blowing agent preparation according to the invention has alower decomposition temperature and higher gas yield than1,4-butanediol-bis-(carbonic acid ester-benzoic acid anhydride). It isimportant to note that the decomposition curve of the blowing agentpreparation according to the invention ascends in almost a straightline. This indicates that the mixture according to the invention tendsto decompose more uniformly.

EXAMPLE 2

a. 20.0 kg of polycarbonate granulate obtained from bisphenol A with arelative viscosity of 1.287 (0.5% solution in methylene chloride),("Makrolon 2800", Manufacturers Bayer AG) were carefully dried (14 hoursat 105° C) and then thoroughly mixed with 540 g of the blowing agent No.2 of Example 1 (2.7%, by weight, based on the mixture ready for use).This mixture was processed into foam plates in a commercial thermoplastfoam injection moulding machine (TSG machine, e.g. Structomatmanufactured by Seimag). Temperature profile: 250°/270°/290°/300° C.Plates: 80 cm × 40 cm × 10 mm thickness, d=0.75 g/cm³. The plate shapedmould was completely filled with foam and the moulded plates showed nosigns of discolouration. The plates had a uniform pore structure intransverse and longitudinal section. Test samples measuring 120 mm × 15mm × 10 mm cut out of the plates were found to have an impact strengthof about 35 KJ/m² determined according to DIN 53 453.

b. 20.0 kg of polycarbonate granulate of bisphenol A with a relativeviscosity of 1.287 (0.5% solution in methylene chloride) ("Makrolon2800," Manufacturers: Bayer AG) were carefully dried (14 hours, 105° C)and then thoroughly mixed with 500 g of 1,4-butanediol-bis-(carbonicacid ester-benzoic acid anhydride) (2.5%, by weight, based on themixture ready for use). This mixture was processed as indicated inExample 2a. Temperature profile: 270°/290°/310°/300° C, plates 80 cm ×40 cm × 10 mm thickness, d=0.75 g/cm³.

The plate mould was completely filled with foam and the platesthemselves showed no signs of discoloration. In longitudinal section,the plates were clearly seen to have an uneven pore structure at theflow ends. Samples measuring 120 mm × 15 mm × 10 mm cut out of thecentre of the plates had an impact strength of about 25 KJ/m² accordingto DIN 53 453.

EXAMPLE 3

20.0 kg of polyamide granulate produced by polycondensation ofcaprolactam ("Durethan BK 30 S", Manufacturers: Bayer AG) were carefullydried and then processed with 540 g of the substance according to theinvention (2.7%, by weight, based on the finished mixture) in a TSGmachine as indicated in Example 2 a). Temperature profile:225°/240°/260°/260° C, plates: 80 cm × 40 cm × 10 mm thickness. Theplate mould was completely filled with foam. The plates showed no signsof discoloration and had a finely porous, uniform foam structure intransverse and longitudinal section. Their density was d=0.73 g/cm³.

EXAMPLE 4

20.0 kg of granulate of polybutylene terephthalate ("Pocan PBT",Manufacturers: Bayer AG) were carefully dried and then thoroughly mixedwith 540 g (2.7%, by weight, based on the finished mixture) of thesubstance according to the invention and then processed on a TSG machineas described in Example 2a. Temperature profile: 225°/240°/260°/ 250° C,plates 80 cm × 40 cm × 10 mm thickness. The mould of the plate wascompletely filled with foam. The foam plates showed no signs ofdiscoloration. They had a uniform, finely porous foam structure inlongitudinal and transverse section. Their density was d = 0.74 g/cm³.

EXAMPLE 5

20.0 kg of granulate of a thermoplastic compound produced frompolyphenylene ether and impact resistant polystryene ("Noryl, FN 215",Manufacturers: General Electric) were carefully dried and thenthoroughly mixed with 700 g of the substance according to the invention(3.5%, by weight, based on the finished mixture) and processed in a TSGmachine as described in Example 2a. Temperature profile:210°/230°/250°/250° C, plates: 80 cm × 40 cm × 10 mm thickness. Theplate mould was completely filled with foam. The plates showed no signsof discoloration. They had a uniform fine porous foam structure inlongitudinal and transverse section. Their density was d = 0.72 g/cm³.

We claim:
 1. Blowing agent mixture consisting of from 85 - 60%, byweight, of 1,4-butanediol bis-(carbonic acid ester-benzoic acidanhydride) and from 15 - 40%, by weight, of silicon dioxide.
 2. Blowingagent mixture according to claim 1, characterised in that the siicondioxide has a surface area according to B.E.T. of from 50 to 400 m² /g.3. Blowing agent mixture according to claim 2, characterised in that thewater content of the silicon dioxide is less than 1.5% by weight.